Patent GB-812498-A (GB)
Title: Method for the purification of esters of acrylic and methacrylic acids
IPC: C07C69/54
Filed: 1957-02-13
Abstract: An aliphatic acrylate or methacrylate ester substantially free from alcoholic impurities is obtained from a mixture containing such ester and an aliphatic alcohol (as defined below) by reacting such mixture with boric acid at elevated temperature, said boric acid being added to the mixture in an amount at least sufficient to react with the alcohol to form the borate ester of the alcohol, removing the resulting water of esterification, and recovering the acrylate or methacrylate ester by distillation.  The term aliphatic alcohol is defined as an alcohol having an hydroxy group attached to an aliphatic radical and includes cycloaliphatic alcohols.  The process is particularly suitable for the purification of aliphatic esters of acrylic and methacrylic acid derived from monohydric alcohols having a boiling point of 115 DEG  C. or higher.  These alcohols can be alkyl, cycloalkyl, alkoxyalkyl, alkoxyalkoxy alkyl, aralkyl, aryloxyalkyl or aralkoxyalkyl containing 4 or more carbon atoms, and may be primary or secondary alcohols.  The boric acid is preferably used in slight excess, e.g. 30 per cent excess over the stoichiometric amount required to form the borate ester and the removal of the water of esterification can be aided by means of an entraining agent for water, e.g. diisopropyl ether, benzene, toluene, or chloroform. The recovery of the acrylate ester may be effected by heating the mixture to boiling preferably under reduced pressure and distilling off the acrylate ester.  The borate ester residue in the still kettle can be hydrolysed with water to regenerate the alcohol and the boric acid and the hydrolysed mixture distilled to recover the alcohol as the water-alcohol azeotrope leaving the boric acid in the residue.  The boric acid can be recovered for re-use by dissolving the residue in hot water and crystallizing the boric acid. When the process is applied to mixtures of acrylate or methacrylate esters which contain free organic or inorganic acids it is desirable to neutralize such acid before the addition of the boric acid.  This may be effected with an inorganic basic compound such as sodium carbonate, sodium hydroxide, or sodium acetate either in the solid form or as an aqueous solution.  When an aqueous solution is used phase separation occurs into an aqueous and an organic layer, the acrylate ester and alcohol and other organic materials, e.g. azeotrope formers such as diisopropyl ether or benzene, and polymerization inhibitors, e.g. hydroquinone, methylene blue, or phenothiazine, separating into the organic phase, and water, acidic condensing agent such as benzene sulphonic acid or sulphuric acid, and water-soluble products separating into the aqueous phase.  The aqueous phase should be removed or decanted from the mixture and the boric acid added only to the organic phase.  The process can be applied to batch, semi-continuous or continuous operation and a flow sheet is given to illustrate the application to a continuous process for the production and purification of acrylate esters obtained by esterification of acrylic acid with about 10 per cent molar excess of the esterifying alcohol in the presence of an esterification catalyst, entraining agent, and polymerization inhibitor.  Examples are given for the application of the process to the purification of tridecyl acrylate, 2-ethylbutyl acrylate, ethylene glycol monophenyl ether acrylate, 2-ethylhexyl methacrylate, n-decyl methacrylate, tridecyl methacrylate, and diethylene glycol monobutyl ether acrylate, respectively, the ester-alcohol mixture used in each case being formed by esterification of acrylic or methacrylic acid with an excess of the appropriate alcohol in the presence of diisopropyl ether, sulphuric acid, and a polymerization inhibitor and the reaction mixture being neutralized in each case by means of sodium carbonate before the addition of boric acid.